Some modern vehicles employ a high pressure fuel injection system to improve the efficiency and operation of the engine. These systems include an intank supply pump and a high pressure pump that supplies fuel at an elevated pressure to a fuel rail. The fuel rail distributes the high pressure fuel to fuel injectors mounted either directly at the combustion chamber the.
The supply pump is generally located in a fuel tank and the high pressure pump is situated on the engine at a distance from the fuel rail. Thus the high pressure fuel has some distance to travel at an elevated pressure between the high pressure pump and the injectors. Since most fuel pumps displace more fuel than is needed by the engine, a fuel return is necessary. The fuel return may be by way of a regulator valve at the high pressure pump to the engine.
In some fuel systems, a continuous flow rotary type pump is used and in other systems, a single acting reciprocating pump is used. The reciprocating pump has a plunger that draws fluid into a cylinder when stroked in one direction and expels fluid from the cylinder when stroked in the other direction. Thus the pump delivers a single charge of fuel during each stroking cycle. Systems using either type of pump still utilize a fuel rail for distributing fuel to the individual injectors on the engine.